In accordance with improvement of performance of a vehicle, an engine of the vehicle is located at a highly elevated temperature environment, and thus many parts included in the engine require high durability and the like in the elevated temperature environment. Particularly, many bolts are used in the engine, and use of a material having excellent high temperature characteristics that may endure the elevated temperature environment is required.
For example, a heat-resistant alloy steel, such as SUH660 and SNB16, which contains a large amount of nickel (Ni) or chromium (Cr), and the like, has been developed. Particularly, a 15Cr26Ni1.25Mo alloy, i.e. SUH660, has been widely used. The SUH660 is a precipitation hardening type of heat-resistant alloy steel and has been used as a shaft material in a turbojet engine for aircrafts until now. The SUH660 is also a face-centered cubic austenitic alloy, and has improved tensile strength of about 271 MPa at the elevated temperatures of about 800° C. and thus has improved heat resistance and high temperature characteristics such as formability, weldability, and the like. Accordingly, SUH660 has been used in a heat-resistant bolt for vehicles, special hot tools, and the like.
However, even though SUH660 has the aforementioned advantages, an expensive nickel (Ni) is contained in a content of about 26% and thus the manufacturing cost increases. Further, in accordance with development of an engine technology, a heat-resistant alloy used in the engine is highly desired to endure such elevated temperatures.
The description provided above as a related art of the present invention is just merely for helping understanding of the background of the present invention and should not be construed as being included in the related art known by those skilled in the art.